Solid oxide cells generally include cells designed for different applications, such as solid oxide fuel cells, or solid oxide electrolyser cells. These types of cells are well known in the art. Typically, a solid oxide cell comprises an electrolyte layer sandwiched by two electrode layers. During operation, a temperature from about 400° C. to 1100° C. is used. One electrode is in contact with air whereas the other electrode is in contact with a fuel gas.
Due to cost reasons there is a desire to use inexpensive materials such as stainless steel for the supporting structure for the cell. Such materials are however only long-time stable below 800° C. At such temperatures, the most common cathode formed from LSM (Strontium substituted Lanthanum Manganite) does not have a sufficient activity, and thus other materials are needed, see W. G. Wang, R. Barfod, P. H. Larsen, K. Kammer, J. J. Bentzen, P. V. Hendriksen, M. Mogensen, Proc. of the 8th International Symposium on solid oxide fuel cells (SOFC-VIII), Paris, Apr. 27 to May 2, 2003. S. C. Singhal, M. Dokiya (eds.), p. 400 to 408 (The Electrochemical Society, Pennington, N.J.) (Proceedings volume PV 2003-07).
Other electrode materials are known which have a higher activity than LSM. An example of such a cathode is a composite of La0.6Sr0.4Fe0.8Co0.2O3-δ with cerium-gadolinium oxide (CGO). The area specific resistance (ASR) of such a cathode is around 0.3 Ωcm2 at 600° C., see E. P. Murray, M. J. Sever, S. A. Barnett, Solid State Ionics, 148 27 (2002). Measured on a cone shaped electrode of La0.6Sr0.4Fe0.8Co0.2O3-δ the ASR is around 100 Ωcm2 at 600° C., see K. Kammer, Solid State Ionics, 177 1047 (2006).
For compositions in the Gd0.8Sr0.2Co1-yFeyO3-δ (0≦y≦1.0) system, a stable dual-phase perovskite system could be shown. Said material is suggested for solid oxide fuel cells, see C. R. Dyck, R. C. Peterson, Z. B. Yu, V. D. Krstic, Solid State Ionics, 176 103-108 (2005).
Yuan Ji, Jiang Liu, Tianmin He, Ligong Cong, Jinxia Wang, Wenhui Su, Journal of Alloys and Compounds, 353 257-262 (2003), relates to single intermedium-temperature SOFCs. A combustion synthesis method, the glycerine-nitrate process, was used to prepare all nano-sized materials used in the single SOFC.
High performance LSCF/CGO composite cathodes have been produced in which the Rp of 0.19 Ωcm2 at 600° C. and 0.026 Ωcm2 at 700° C. were obtained on a CGO electrolyte, see Wei Guo Wang, Mogens Mogensen, Solid State Ionics, 176 457-462 (2005).
G. Ch. Kostogloudis, G. Tsiniarakis, Ch. Ftikos, Solid State Ionics, 135 529-535 (2000) relates to the chemical reactivity of perovskite oxide SOFC cathodes and yttria stabilized zirconia.
Even though the ASR value of the composite La0.6Sr0.4Fe0.8Co0.2O3-δ/CGO as obtainable by the prior art is more than 3 times lower then the value of the classical LSM cathode, the ASR at 600° C. is still to high for many applications, and thus there is a strong desire to develop new electrodes with lower ASR values.